fix: update package.json to allow webpack bundling

Author: sis0k0

package.json

@@ -2,7 +2,7 @@
   "name": "nativescript-floatingactionbutton",
   "version": "2.2.6",
   "description": "A NativeScript plugin for Material Design Floating Action Button.",
-   "main": "fab.js",
+   "main": "fab",
   "nativescript": {
     "platforms": {
       "android": "1.5.0",